Ultrasonic lesion feedback, antipop monitoring, and force detection

ABSTRACT

An ablation catheter comprises: an elongated catheter body extending longitudinally between a proximal end and a distal end along a longitudinal axis; a distal member disposed adjacent the distal end, the distal member including an ablation element to ablate a biological member; one or more acoustic transducers disposed in the distal member and each configured to direct an acoustic signal toward a respective target ablation region and receive reflection echoes therefrom; and an acoustic redirection member disposed in the distal member to at least partially redirect the acoustic signal from at least one of the acoustic transducers toward a tissue target. The distal member includes a most-distal portion, a proximal portion, and a deflectable portion between the most-distal portion and proximal portion to permit deflection between the most-distal portion and proximal portion of the distal member. The transducers and redirection member are mounted on opposite sides of the deflectable portion.

This application claims priority from U.S. Provisional PatentApplication No. 61/636,767, filed on Apr. 23, 2012, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to catheters for ablation or thelike and, more particularly, to a disposable catheter with low COGS,ultrasonic lesion feedback, antipop monitoring, and force detection, andto a dual transducer with forward and side looking ultrasonic lesionfeedback and optional force detection.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention provide a force sensing catheter andsupporting system for therapeutic or diagnostic applications. A catheterincludes an elongated flexible catheter body having a distal end and aproximal end, a therapeutic or diagnostic tip on the distal end of thecatheter body, and a catheter control handle or manipulation mechanismcoupled to the proximal end of the catheter body. The tip regionincludes a most distal rigid tip portion mounted upon a more proximalabutting semi-rigid tip portion, the semi-rigid portion having knownstiffness versus deflection (providing some useful tissue conformingbehavior of the semi-rigid tip portion); and (i) an acoustic mirror,window, or membrane, and (ii) an acoustic transducer. The transducer isarranged to emit and receive an acoustic beam or ping which has been atleast partially reflected from the mirror, window or membrane. Forcesapplied to the tip by contacting tissue cause the most distal rigid tipportion to deflect as a rigid whole because it is mounted upon the moreproximal semi-rigid deflectable tip portion which angularly and axiallydeflects slightly but detectably. One of the (i) mirror/window/membraneor (ii) transducer is mounted in the most distal rigid portion and theother is mounted proximally to some or all of the semi-rigid portion(such as, for instance, a rigid proximal portion of the tip region). Thetransducer is thereby capable of detecting axial and/or angular bendingdeflections via the changing amplitude and/or time delay of reflectionsof the acoustic beam or ping reflected from the most distal rigid tipportion mounted upon and bodily movable upon said semi-rigid butdeflectable intervening more-proximal tip portion. The catheter systemcomputes from models or retrieves from lookup tables the force(s) whichcorrelate with the system-observed tip deflections via the known angularstiffness and axial stiffness of the semi-rigid portion. The systemreports or otherwise utilizes the force for a procedural control,recording, or safety reason.

The inventive catheter will provide all of antipop monitoring, lesionfeedback, and preferably both bending and axial force componentmagnitudes and their net vector sum. In principle, any so-equippedcatheter may provide any one or more of lesion progress feedback,antipop monitoring, and force detection. In addition, the catheter mayinclude dual opposed transducers, one forward looking and onebackward/side looking via reflective redirection of its beam, whichshare a common attenuative backer block between them. By placing theseopposed-facing transducers on a flexible tip one may also optionallyutilize the ultrasound/mirror arrangement to measure force upon tissue.Such a device gives two excellent views of possible tissue targetsrather than a single compromise view such as that given by 45 degreedevices.

In accordance with an aspect of the present invention, an ablationcatheter with acoustic monitoring comprises: an elongated catheter bodyextending longitudinally between a proximal end and a distal end along alongitudinal axis; a distal member disposed adjacent the distal end, thedistal member including an ablation element to ablate a biologicalmember at a target region outside the catheter body; one or moreacoustic transducers disposed in the distal member and each configuredto direct an acoustic signal toward a respective target ablation regionand receive reflection echoes therefrom; and an acoustic redirectionmember disposed in the distal member to at least partially redirect theacoustic signal from at least one of the acoustic transducers toward atissue target. The distal member includes a most-distal portion, aproximal portion, and a deflectable portion between the most-distalportion and the proximal portion to permit deflection between themost-distal portion and the proximal portion of the distal member, thedeflectable portion being more deflectable than at least one of themost-distal portion or the proximal portion. For the distal member, (i)the one or more acoustic transducers are mounted to the most-distalportion and the acoustic redirection member is mounted to the proximalportion, or (ii) the one or more acoustic transducers are mounted to theproximal portion and the acoustic redirection member is mounted to themost-distal portion of the distal member.

In some embodiments, the most-distal portion of the distal member has noaxial deflection and no bending deflection occurring within its ownconfines. The proximal portion of the distal member has no axialdeflection and no bending deflection occurring within its own confines.The deflectable portion of the distal member, within its own confines,permits at least one of axial deflection along the longitudinal axis orbending deflection between the most-distal portion and the proximalportion of the distal member. The axial deflection is less than about 1mm under an axial force of less than about 100 grams. The bendingdeflection is less than about 10 degrees under a bending moment of about200 gram-millimeters. The deflectable portion of the distal memberincludes one of a laser machined metallic tube with cuts, a metallictube with cuts machined by wet etching, a metallic tube with cutsmachined by EDM (electric discharge machining), a polymeric tube, abraided tube, a woven tube, a convoluted tubular member, a mesh tube, ahoneycombed tube, a wave washer, or a tubular member having bellows. Atleast one of the acoustic transducers is configured to detect adeflection via at least one of an amplitude change or a phase ortime-delay change of a reflection of an acoustic signal reflected backfrom the acoustic redirection member.

In specific embodiments, an acoustic reflection member is mounted to thesame portion of the distal member as the acoustic redirection member andbeing configured to partially reflect an acoustic signal from at leastone acoustic transducer of the acoustic transducers back to the at leastone acoustic transducer. The at least one acoustic transducer isconfigured to detect a deflection via at least one of an amplitudechange or a phase or time-delay change of a reflection of the acousticsignal reflected back from the acoustic reflection member. The acousticreflection member comprises one of a partially reflective membrane or apartially reflective prism.

In some embodiments, a controller is operable to determine, based on thedetected deflection and a related force-deflection relationship of thedeflectable portion of the distal member, a force between the distalmember and the biological member. The acoustic signal comprises anacoustic beam or an acoustic ping. The one or more transducers comprisea sideways-redirected acoustic transducer to produce an acoustic signalthat is redirected in a beam emanation direction nonparallel to thelongitudinal axis to monitor a sideways-formed lesion, and aforward-directed acoustic transducer to produce another acoustic signalthat is directed in another direction generally parallel to thelongitudinal axis to monitor a forward-facing lesion, respectively.

Another aspect of the invention is directed to an acoustic monitoringmethod for an ablation procedure using an ablation catheter whichincludes an elongated catheter body extending longitudinally between aproximal end and a distal end along a longitudinal axis; a distal memberdisposed adjacent the distal end, the distal member including anablation element to ablate a biological member at a target regionoutside the catheter body; one or more acoustic transducers disposed inthe distal member and each configured to direct an acoustic signaltoward a respective target ablation region and receive reflection echoestherefrom; and an acoustic redirection member disposed in the distalmember to at least partially redirect the acoustic signal from at leastone of the acoustic transducers toward a tissue target. The distalmember includes a most-distal portion, a proximal portion, and adeflectable portion between the most-distal portion and the proximalportion to permit deflection between the most-distal portion and theproximal portion of the distal member, the deflectable portion beingmore deflectable than at least one of the most-distal portion or theproximal portion. For the distal member, (i) the one or more acoustictransducers are mounted to the most-distal portion and the acousticredirection member is mounted to the proximal portion, or (ii) the oneor more acoustic transducers are mounted to the proximal portion and theacoustic redirection member is mounted to the most-distal portion of thedistal member. The method comprises: ablating the biological member atthe target region with the ablation element; directing one or moreacoustic signals to the biological member and receiving reflectionechoes from the biological member by the one or more acoustictransducers, the one or more acoustic signals including an acousticsignal directed toward the tissue target by the acoustic redirectionmember; and detecting a deflection between the most-distal portion andthe proximal portion of the distal member based on reflection of anacoustic signal reflected back to at least one of the acoustictransducers.

In some embodiments, the detecting comprises detecting a deflection viaat least one of an amplitude change or a phase or time-delay change of areflection of an acoustic signal reflected back from the acousticredirection member to at least one of the acoustic transducers. In someother embodiments, the detecting comprises detecting a deflection via atleast one of an amplitude change or a phase or time-delay change of areflection of an acoustic signal reflected back from an acousticreflection member to at least one of the acoustic transducers, theacoustic reflection member being mounted to the same portion of thedistal member as the acoustic redirection member and partiallyreflecting the acoustic signal back to the at least one acoustictransducer.

In specific embodiments, the acoustic monitoring method furthercomprises determining, based on a detected deflection and a relatedforce-deflection relationship of the deflectable portion of the distalmember, a force between the distal member and the biological member. Thedirecting comprises at least one of: directing a first acoustic signalfrom a first acoustic transducer in a direction generally parallel tothe longitudinal axis to the acoustic redirection member which redirectsthe first acoustic signal in a transverse direction nonparallel to thelongitudinal axis to monitor a sideways-formed lesion; or directing asecond acoustic signal from a second acoustic transducer in a forwarddirection generally parallel to the longitudinal axis to monitor aforward-facing lesion. Directing one or more acoustic signals to thebiological member and receiving reflection echoes from the biologicalmember by the one or more acoustic transducers comprises at least one ofacoustic lesion feedback of the biological member being ablated, atissue thickness measurement in a region of the biological member beingablated, a tissue proximity measurement in a region of the biologicalmember being ablated, a pre-pop warning of the biological member beingablated, or a pre-pop detection of the biological member being ablated.

These and other features and advantages of the present invention willbecome apparent to those of ordinary skill in the art in view of thefollowing detailed description of the specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows an inventive catheter tip region depicting ultrasoniclesion feedback plus simultaneous force measurement using the sametransducer and acoustic mirror tip deflected upon endocardial tissue.

FIG. 1B shows plots of axial and radial (angular) deflection versusdetected acoustic reflection amplitude from the mirror.

FIG. 2 is a schematic diagram of an ablation apparatus incorporating theablation catheter tip of FIG. 1A.

FIG. 3 shows another catheter tip region illustrating a dual transducerwith forward and side looking ultrasonic lesion feedback and optionalforce detection.

FIG. 4 shows an example of using two separate components for tissueimages and deflections respectively.

FIG. 5 shows another example of using two separate components for tissueimages and deflections respectively.

FIG. 6 shows an example of a mirror having a microstructured surface inthe form of a three holes at the mirror periphery distributed about 120degrees apart from each other.

FIG. 7 shows an example of a mirror having a microstructured surface inthe form of an array of holes along diagonal(s).

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description of the invention, reference ismade to the accompanying drawings which form a part of the disclosure,and in which are shown by way of illustration, and not of limitation,exemplary embodiments by which the invention may be practiced. In thedrawings, like numerals describe substantially similar componentsthroughout the several views. Further, it should be noted that while thedetailed description provides various exemplary embodiments, asdescribed below and as illustrated in the drawings, the presentinvention is not limited to the embodiments described and illustratedherein, but can extend to other embodiments, as would be known or aswould become known to those skilled in the art. Reference in thespecification to “one embodiment,” “this embodiment,” or “theseembodiments” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the invention, and the appearances ofthese phrases in various places in the specification are not necessarilyall referring to the same embodiment. Additionally, in the followingdetailed description, numerous specific details are set forth in orderto provide a thorough understanding of the present invention. However,it will be apparent to one of ordinary skill in the art that thesespecific details may not all be needed to practice the presentinvention. In other circumstances, well-known structures, materials,circuits, processes and interfaces have not been described in detail,and/or may be illustrated in block diagram form, so as to notunnecessarily obscure the present invention.

In the following description, relative orientation and placementterminology, such as the terms horizontal, vertical, left, right, topand bottom, is used. It will be appreciated that these terms refer torelative directions and placement in a two dimensional layout withrespect to a given orientation of the layout. For a differentorientation of the layout, different relative orientation and placementterms may be used to describe the same objects or operations.

Exemplary embodiments of the invention, as will be described in greaterdetail below, provide apparatuses, methods and computer programs forultrasonic lesion feedback, antipop monitoring, and net force magnitudeand direction detection.

Ultrasonic Feedback with Single Acoustic Transducer in Semi-RigidCatheter Tip

One aspect of this invention is to utilize an acoustic lesion feedbacktransducer to also measure distortions of a distortable tip having known(but very slight) spring behavior. How to do that for both axial andbending forces using a single spring is not obvious if one has in mind avery flexible tip made flexible to conform to tissue such as a Coolflex™tip. Thus, tissue conforming tips teach away from the invention.

Embodiments of the invention utilize a minimally flexible or semi-rigidtip (defined below) which is just flexible enough that its slightbending/compression with loading can be detected using atransducer/mirror arrangement; however, it is not so flexible that theultrasonic beam angles between transducer and mirror changesignificantly (to a gross tissue conforming extent). In this way, onecan track the force-induced slight axial compression and radial bendingdeflections as small time-delay changes (for axial deflections) andsmall reflection magnitude changes (for radial deflections). Further,one can retain in view, despite the deflections, the bulk of the tissueechogram coming from within the tissue which varies only with tissuenecrosis or microbubbling. Note specifically that the semi-rigid tip isnot useable to achieve gross tissue conformance. It will be apparent toone skilled in the art that angulating reflecting or redirecting mirrorswill result in both time-delay changes and amplitude changes and theseeffects can combine to cause reflective peaks to both predictablybroaden/narrow and/or to change amplitude depending on the geometriesinvolved.

It is critical that this catheter tip, to the human eye, is essentiallyrigid even though it will have laser cuts (or some other features offlexibility) which allow very slight distortions just large enough thatthey can be acoustically detected and correlated to a tiny deflection ofa “stiff spring” section. We anticipate an angular distortion on theorder of a degree or a few degrees (e.g., ±about 5 degrees) maximum andan axial distortion on the order of a fraction of a millimeter (e.g., afew hundred microns).

In technical terms, the term “semi-rigid” means that one needs to use adeflection-detecting transducer which has a high enough frequency suchthat the maximum axial distortion is on the order of at least about ahalf wavelength. For example, one may use a transducer which is centeredat about 10 MHz to about 16 MHz. For typical axial load ranges of about5-50 grams, it may be desirable to have about a half wavelength of axialdeflection, and for sideways radial loads of the same magnitude, it maybe desirable to have angular distortions of about one degree or a fewdegrees. In a preferred embodiment, an A/D (analog-digital) digitizerhas a minimum digitization rate of 100 MHz and a rate of about 200-500MHz with at least effective 8-bits of amplitude resolution is preferred.The higher sampling frequency gives better time (versus sampleamplitude) resolution so that one can detect small axial distortionscausing time delay changes as well as small angular distortions causingmostly amplitude changes.

FIG. 1A shows a sectional view of an ablation catheter according to anembodiment of the invention. The catheter includes a flexible body 1 dconnected to an ablator tip 1 which has a rigid most-distal tip portion(acoustic mirror portion) 1 a including an acousticreflection/redirection member (mirror, window, membrane) 2, anintermediate more-proximal semi-rigid portion 1 b acting as a stiffspring, and a rigid most proximal tip portion 1 c. Ideally, the rigidmost-distal portion 1 a has no internal axial deflection and no internalbending deflection (occurring within its own confines) and the rigidproximal tip portion 1 c has no internal axial deflection and nointernal bending deflection (occurring within its own confines). Allsuch bending and axial deflections are arranged to occur in the springsection 1 b (within its own confines) between the most-distal tipportion 1 a and the proximal tip portion 1 c. The mirror reflectingsurface is typically metallic and the mirror can be nonfocusing orfocusing. The ablator tip 1 may be an RF ablator tip wherein themost-distal portion 1 a is an RF electrode as the ablation member (e.g.,made of metal such as a platinum alloy), or the ablator tip 1 mayinclude one or more RF electrodes such as ring electrodes to provide RFablation.

In FIG. 1 a, the ablator tip 1 is depicted pressed into an endocardium 4from a blood chamber 5 by the action of a contact force which generallywill have a tangential component along the x-axis and a normal componentalong the y-axis. A directional (emitting in the −x direction here)ultrasonic transducer 3 is shown mounted in the rigid proximal tipportion 1 c. The transducer 3 produces acoustic signals such as acousticbeams or acoustic pings leftwards along a −x beam path off the mirror 2into the tissue 4 to a tissue focus 7 and receives reflection echoesback from the tissue 4, both defined by beam boundaries 6 a and 6 b.Note that the surface of the mirror 2 will slightly move/reorientrelative to the transducer 3 upon tip loading because they are separatedby the slightly flexible spring portion 1 b. FIG. 1A shows a slightbending of the tip, to an angle θ, perhaps a few degrees or so. A lesion4 a is shown being formed in the tissue 4 as would be expected for anirrigated tip 1 with coolant saline 12 emanating from a beam port 11.Thus, the spring deflections are only large enough to detect tip forces(axial x force, radial y force, and/or their vector sum and its angle tothe tip long axis). The deflections are not large enough that the lesionfeedback acoustic behavior is significantly different from that of acompletely rigid acoustic transducer-mirror tip, i.e., the slightdeflections do not shift the lesion feedback beam significantly.

According to one configuration of the catheter device, a totally rigidside-fire mirror tip (no force capability) is capable of lesion feedbackand has shown good tissue spectra upon lesioning. The device has a holeor port 11 out of which the beam 6 a/6 b and the saline 12 emanate. Thatarrangement means that the RF lesion is formed primarily by thesurrounding circumferential lip region of the most-distal tip portion 1a defining the hole or port 11 and somewhat by the saline 12 emanatingtherefrom. That also means that the tissue being lesioned has a freeunderwater surface as opposed to a physically trapped cooled-ablatorpressing upon it. That might undesirably allow for easier boiling. Wehave shown that an open port 11 can be made to work with sufficientirrigation flow; however, this disclosure also covers a port being aconductive impermeable or permeable membrane or window or mesh which canitself deliver some RF energy. A nonconductive membrane is also withinthe scope of this disclosure.

The acoustic reflection/redirection member (mirror, window, or membrane)2 and its movement relative to the transducer 3 form theforce/deflection sensing mechanism. One preferred approach is the use ofan angled (e.g., about 45 degrees as shown) acoustic mirror 2 stood offby a tip-internal saline cavity (between the mirror 2 and the transducer3). We include in the scope of this disclosure the conditioning of themirror (or membrane) surface (or bulk) such as by slight roughening,porosity or shaping so as to improve the mirror's acoustic visibilityand response to orientation/position changes but not so much that welose sensitivity otherwise useable for tissue reflections. The angledmirror, which is arranged to be nearly totally reflective (e.g., about90-98%) but not 100% reflective, can thereby return both a virtuallyunaltered tissue reflection as well as a weaker tissue-nonobscuringreflection from the mirror itself.

Alternatively one may provide the above mirror for tissue feedback andalong the same beampath and also inside the tip also provide a low losswindow, membrane, or prism of TPX polymer whose job it is to provide anormally orthogonal weak reflector to detect deflections. FIG. 4 showsan example of using two separate components for tissue images anddeflections respectively. The ablator tip 1 uses the acoustic mirror 2to redirect the acoustic signal from the transducer 3 for tissue imagesand uses another member 402 to detect deflections. The member 402 may bea membrane of TPX (polymethylpentene) polymer which is more than 90%transparent but not 100% transparent. The mirror 2 and the membrane 402form an acoustic reflection/redirection member. FIG. 5 shows anotherexample of using two separate components for tissue images anddeflections respectively. The ablator tip 1 uses the acoustic mirror 2to redirect the acoustic signal from the transducer 3 for tissue imagesand uses another member 502 to detect deflections. The member 502 may bea solid prism of TPX polymer which is more than 90% transparent but not100% transparent. The mirror 2 and the prism 502 form an acousticreflection/redirection member.

The semi-rigid tip portion 1 b may be made in a manner somewhat similarto a lasered Coolflex™ tip (i.e., using Nitinol™ tubing and a laser beamcutter to form through-thickness cuts or partial-thicknesscuts/grooves). In the example shown in FIG. 1A, multiple rows ofcircumferential cuts are staggered to form the semi-rigid tip portion 1b. The major difference is that the laser cuts in this case are arrangedto offer only very slight distortions (axial and/or angular) of thelasered member and are highly localized along the tip length dimension.The minimal distortion, semi-rigid spring member 1 b can be provided inmultiple ways and the following are a few examples. Some of these do noteven involve laser cutting.

Approach 1—Use a laser machined metallic tube with significantly fewerlaser cuts than a Coolflex™ flexible tip. The structure becomes muchstiffer and acts as a stiff-spring to provide axial deflection of lessthan about 1 mm, preferably less than about 0.5 mm but more than about0.125 mm and angular deflection of less than about ±10 degrees,preferably less than about ±5 degrees. Alternatively, the metallic tubemay be machined in any manner such as by wet etching or EDM (electricdischarge machining).

Approach 2—Use cuts which do not overlap as much, thereby reducingcumulative distortion. The structure becomes much stiffer.

Approach 3—Use a thicker tubing than a Coolflex™ flexible tip. Thestructure is linearly stiffer with increasing thickness approximately.

Approach 4—Rather than laser cutting of tubing, use instead a convolutedor bellows-like tubular entity, whether metallic, ceramic, glass orpolymeric (e.g., uncut bellows-like electrodeposited shell tips, wavewashers).

Approach 5—Make a flexible tip out of elastic braid to form a braided orwoven tube, a mesh structure, a honeycombed sheet, or a polymeric tube.A tube is a body having an interior cavity, two open opposed ends, alength, and a cross-sectional shape mountable in or on the tip, thecross-sectional shape not necessarily round.

In FIG. 1A, the mirror 2 is mounted in the most distal rigid tip portion1 a and the transducer 3 is mounted in the proximal rigid tip portion 1c. In another embodiment, the transducer 3 is mounted in the most distalrigid tip portion 1 a and the acoustic reflection/redirection member(mirror, window, or membrane) is mounted at the proximal rigid tipportion 1 c or at the more proximal end of at least some of theconnected semi-rigid deflectable portion 1 b, the acoustic beam or pingtraveling through the interior space of at least some of the deflectablesemi-rigid portion 1 b. The space for the acoustic path of the beambetween the acoustic reflection/redirection member 2 and the transducer3 includes or is filled with a flowable or deflectablelow-acoustic-attenuation material such as saline or a low loss polymersuch as a urethane or TPX or a combination thereof.

Typically, an operating transducer frequency of the transducer 3 is inthe range of about 2 to 50 MHz with a preferred frequency in the rangeof about 10 to 30 MHz as a tradeoff between axial resolution andmanufacturability. RF ablation and ultrasonic pinging are arranged tooccur substantially separately in time to avoid their interfering witheach other. Any one or more of RF ablation or ultrasonic pinging may besynchronized or gated using a biological signal such as an ECG or EGMsignal in addition to or instead of being synched to each otherdirectly.

An example of the acoustics amplitude and/or time-phase variation versustip forces is shown in FIG. 1B. The axial force component upon the tipalong the ±x axis is the easiest to describe. Essentially any acousticspectrum feature which occurs at a point in time will be shifted by Δt(see shifting of graph 8 in FIG. 1B) by the application of the axialforce component. This is simply because the transducer 3 is eitherslightly closer to or slightly further from the mirror 2 (whose ownreflection can be seen independent of the tissue reflections) forcompression and tension tip loads, respectively. This phenomenon willtake place even if there is also a few degree angular A for bending. Thebending reflection variation behavior is approximately shown as a plot 9at a particular axial deflection. Essentially over the narrow allowable0-70 gram 0-5 degree or so bending range, the behavior will be slightlycurvilinear as depicted. Although in the actual case, both axial andbending forces are simultaneously applied, what is occurring is thatbecause of the heartbeat and/or breathing cycle, we will, over the timeof seconds, be essentially plotting a back and forth orbital path suchas the repeating path 13 shown in FIG. 1B. We anticipate that havingthat path information will allow us to deconvolute the axial and radialdeflection components whatever combination they take. The transducer 3can detect the deflection (axial and angular) via at least one ofamplitude change or phase change of reflection of an acoustic signalreflected back from the acoustic reflection/redirection member 2. In apreferred embodiment, the mirror angulation itself causes minimaltime-delay change (but a large amplitude change) and if desired, byknowing the amplitude change (and bending degree), one can actuallysubtract out the minimal time-delay change due to bending such that allremaining time delay change is due to axial deflection. The inventorshave demonstrated this ability albeit the correction is small.

In US2012/0265069 (which is incorporated herein by reference in itsentirety), we taught an acoustically transparent RF tip madesubstantially entirely of carbon (e.g., at least about 90% carbon byvolume) having an acoustic impedance between that of the transducer andthat of the tissue. As applied in this case, the rigid most-distalportion 1 a may be carbon based such that there is no need for an openport 11, resulting in the delivery of uniform RF. One would still haveirrigated saline very close by or upon the heated tissue surface.Furthermore, the mirror 2, with a carbon tip portion 1 a, may be athinfilm metal-on-carbon laminate.

The catheter provides ablation capability in addition to at least one of(a) data regarding a formed or forming lesion, (b) data regarding aninterface or tissue thickness, (c) data regarding a degree oftransmurality of a lesion in a tissue layer, and (d) data regardingpotential or actual pop activity. Either of lesion-feedback or poppotential is detected acoustically by an acoustic beam which enterstissue through the acoustic reflection/redirection member 2 (mirror,window or membrane) or an open hole or port 11 in the tip 1.Furthermore, (i) any one or more of force, a lesion progress parameteror a pop parameter are reported to the user in any form; (ii) any one ormore of force, a lesion progress parameter or a pop parameter areinternally utilized by the system in any form; and (iii) any one or moreof force, a lesion progress parameter or a pop parameter are recorded orremotely communicated in any form. By allowing the acoustic beam or pingto enter tissue, the system also or instead reports or utilizes any oneor more of: (i) lesioning behavior or state, (ii) prepop behavior orstate, and (iii) proximity or orientation to tissue. Any one or more ofthe force, pop or lesion-feedback capabilities may be activated and/ordeactivated via software uploads, network communications, or customerinput, whether by the system user, by a connected system or network orby a remote support person. Any one or more of force, a lesion progressparameter, or a pop parameter may be utilized as feedback to the systemor user for a control, safety, or logging reason.

If a customer has possession of a transducer-bearing catheter, we canprovide or activate software, even remotely, which can perform any oneor more of: (a) reporting force, (b) providing anti-pop monitoring, and(c) reporting lesion depth. Since upon pinging we get all theinformation pertaining to the tissue and the moving mirror, we are notadding anything to procedure time. The algorithm to do the distortionmeasurement (force measurement) is actually much simpler than thelesion-depth algorithm or the anti-pop algorithm. We can providesoftware upgrade on-demand at the moment the practitioner decides he/shewants that modality. It would be turned on and charged to the customer'saccount at the same time.

We stated that macroscopically conforming lasered bending tips teachaway from the present invention. That is because if one simply puts theinventive transducer and mirror on the opposite (far) end of such aflexible laser tip, the tissue-conformance bending is so large (tens ofdegrees bending sometimes) that it would be very difficult to retain areasonable tissue-echo spectrum from the tissue or, for that matter, anyecho off the mirror back to the transducer over such a huge range.Although one could put the transducer and mirror closer together toovercome this issue, when one does that, one is removing some of theuseful standoff distance which allows easy identification of the mirrorecho beyond the transducer ringing noise. However the invention is notfundamentally incompatible with highly conforming macroscopicallybending tips. By placing the mirror closer to the transducer, one couldtolerate more tip bending as long as the transducer employed has a shortenough ringdown.

We also include in the scope of this invention the mirror 2 (or windowor membrane) having a microstructured surface such as that made by lasermachining or etching. The idea is to place features on/in the mirrorsurface either locally or across the mirror face (a) which do notsubstantially interfere with tissue echoes such as by consuming only avery small percentage of the area of the mirror (e.g., a few percent atthe midregion for example) and (b) which enhance the changes in acousticreflection behavior (amplitude and/or phase) with mirror tilting and/oraxial motion. For example, one could laser drill an array of holes atever increasing angles from 90 degrees into the mirror surface. Theability to acoustically “see” the bottoms of the various holes dependson whether that particular angled hole is “pointing” at the transducerat that particular state of bending load. Such a hole array could beplaced in the central mirror region and/or concentrated upon a fewradial lines running from mirror center to edge. FIG. 6 shows an exampleof a mirror 2 having a microstructured surface in the form of a threeholes at the mirror periphery distributed about 120 degrees apart fromeach other. FIG. 7 shows an example of a mirror 2 having amicrostructured surface in the form of an array of holes alongdiagonal(s). The holes come/go from acoustic view versus tilt angle. Thehole bottoms provide strong orthogonal reflectors at zero degrees.Varying hole depth could allow identification of any specific hole.

The mirror 2 (or window or membrane) may also be focusing or refractingof acoustics wherein the acoustic reflections from the mirror vary withangle as the reflection/focus/refraction behavior versus anglesystematically changes.

One feature the invention is a combined acoustic and optical solutionwherein the acoustics do the lesion feedback, the antipop monitoring,and only the axial part of force detection. The mirror is opticallycoated with an optical interference film system such that its opticalreflectivity (or reflected color) changes with mirror tilt angle. Inthis case, a small optical fiber/optical lens/light source wouldilluminate the mirror likely in the middle from a standoff distancelarger than the maximum tip compression. The reflected light would beanalyzed for color and/or amplitude. Thus we get bending force opticallyfrom the mirror and we get axial force acoustically from the mirror.

We again expect and know that when an intracardiac or other therapeuticor diagnostic catheter is in the body that the heartbeat motion, theblood flow and the breathing of the patient all cause periodicvariations in catheter tip contact angle and force. We include here inour inventive scope, most particularly for those applications involvinglesion or pop feedback, the recording or use of known instrumentedbreathing rates and heartbeat rates in order to account for theireffects upon echograms. For example, echograms could be time-sampledbased on the heartbeat deduced from the cyclic force data therebyobtaining echograms at known heartbeat phase angles. As an alternativeone can record enough echograms often enough so that such periodicitiescan be discovered purely from the echogram data and the appropriatecompensations made therefore.

FIG. 2 is a schematic diagram of an ablation apparatus incorporating theablation catheter tip of this disclosure. An ablation catheter 110includes a control handle 116, and an elongated catheter body 112 havinga distal region 114 adjacent a distal end 118. The distal region 114includes any of the ablation tips shown and described herein (e.g.,ablator tip 1 in FIG. 1A or ablating tip 302 in FIG. 3). The catheter110 is connected with an ablation energy source 120 such as an RFgenerator, and with an irrigation fluid source 124 to provide anirrigation and tip-cooling fluid. A transducer pinger 128, which mighthave more than one channel, transmits and receives pinging energy suchas that delivered to or received from acoustic transducer(s) (e.g., 3 inFIG. 1A or 305 a and 305 b in FIG. 3). A control unit or controller 130is provided for controlling the ablation and the acoustic pinging duringablation. For instance, the control unit 130 is configured to carry outthe duty cycles for ablation and pinging. An acoustic pinger echoanalyzer 132 is provided to analyze the data collected (e.g., by asoftware or firmware algorithm) from the acoustic transducer(s) toprovide one or more of lesion feedback, tissue thickness or proximitymeasurement, tip contact force monitoring, and pre-pop detection. Theinformation is preferably presented to the operator (e.g., using agraphical user interface) to provide real time assessment of theablation. The information may additionally or alternatively be utilizedby the system itself without operator intervention. Based on a detecteddeflection and a related force-deflection relationship of thedeflectable spring portion 1 b, the control unit 130 can determine theforce between the distal tip 1 and the biological member such as theendocardium 4.

Ultrasonic Feedback with Forward and Side Looking Acoustic Transducersin Semirigid Catheter Tip

FIG. 3 shows another catheter tip region illustrating a dual transducerwith forward and side looking ultrasonic lesion feedback and optionalforce detection. FIG. 3 shows an RF ablation catheter 301 having anablating tip 302 distally mounted on a flexible catheter body 303 havinga lumen. The catheter 301 is shown immersed in blood 311 such as withina heart chamber or some other biological member. The catheter ablationtip portion 302 is depicted resting against a myocardial or ventricularwall 310 which is to receive a lesion 312. It will be noted that thedistal tip portion 302 contains a dual ultrasonic transducer 305 capableof either or both of pinging forwardly along the −x direction ordownwardly (sideways via mirror 307 redirection) in the −y direction.The transducer 305 has a shared common attenuative backer materialportion 305 c on which are mounted opposed piezotransducers 305 a(forward looking) and 305 b (side looking via redirecting acousticmirror 307). Because the transducer piezoelements 305 a/305 b both sharethe same attenuative backer 305 c, we save space inside the tip 302. Theforward firing transducer 305 a forms a beam defined by beam outline 308a/308 b which comes to a forward focus at point 308 also labeled asF_(f). That forward beam passes through a window or hole in the tip bodyin order to pass to focus 308. The side-firing (via mirror 307)transducer 305 b forms a beam which is redirected sideways (−ydirection) in the form of outline 309 a/309 b and coming to a focus atpoint 309 also labeled as point F_(s). The acoustic mirror 307, such asa stainless mirror, is depicted to have a 45 degree angle relative tothe x-axis such that it redirects the sidefire beam 309 a/309 bapproximately at a right angle out of the tip 302 into the target tissue310.

It will be noted in FIG. 3 that the forward-firing beam 308 a/308 btravels through saline 306 a or other acoustically transparent material(such as urethane, silicone, or TPX) before emanating forwardlygenerally along the longitudinal axis to focus point 308. Likewise,sidefire beam 309 a/309 b travels through saline or other acousticallytransparent material 306 b before emanating sideways in a beam emanationdirection to focus point 309 (F_(s)). In a preferred embodiment,materials 306 a and 306 b are saline which is passed through the tip 302also for cooling purposes (such as for tissue surface cooling/irrigationand/or tip cooling). Included within the inventive scope is havingportions of the saline filled region instead or partly filled with theaforementioned transparent, nonfluid, flexible or rigid materials suchas urethane, silicone, or TPX.

The distal ablating tip 302 includes a first ultrasonic transducer 305 aoriented to give a tip-forward view of target tissue 310 (in the forwarddirection along the longitudinal axis, when the tip is end-on to tissue)and a second ultrasonic transducer 305 b oriented to give a tip-sidewaysview of target tissue 310 (acoustic signal being redirected in atransverse direction nonparallel to the longitudinal axis and typicallysubstantially perpendicular to the longitudinal axis) as shown in FIG.3. At least one of the transducers (305 b) directs its acoustic beamupon the acoustic redirection mirror 307 which redirects the acousticbeam to achieve its sideways view of target tissue 310. The transducer305 b and the acoustic mirror 307 are situated on opposite sides of atip spring member 304 of known stiffness which distorts in response to atip load causing an angle and/or distance between the transducer 305 band the mirror 307 to vary with the tip force, the distortions (bendingand axial) each being acoustically detectable and accompanied by acorresponding tip force component. In FIG. 3, the dual transducers 305are mounted to a rigid most-distal tip portion 302 a while the mirror307 is mounted to a rigid proximal tip portion 302 b. The twotransducers 305 a, 305 b are mounted in an opposed fashion such thatthey share a common attenuative backer 305 c rather than separatebackers which would take more space. Each of the transducers isseparately operable via its own electrical interconnections (not shown).

As seen in FIG. 3, the distal tip 302 has lasered slits or slots cutinto it at a localized axial location to form an intermediate semi-rigidspring portion 304. These slots act as a stiff spring such that the moredistal tip portion 302 a can slightly deflect angularly with respect tothe more proximal tip portion 302 b such as around one or both of they-axis and/or z-axis. The semi-rigid portion 304 may also/instead allowsome stiff axial deformation axially along the x-axis. By stiff we meanthat typical tip loads in the range of about 10-100 grams will bend themost-distal tip portion 302 a relative to the proximal tip portion 302 bjust a few degrees at most (less than about 10 degrees, preferably lessthan about 5 degrees). In this manner, even when bent by a tip-load, theside-fire beam 309 a/309 b can still echogenically view the tissue. Thesame can be said for any axial deflection of the stiff spring 304 inthat it may be limited to a fraction of a millimeter or even less (lessthan 1 mm, preferably less than about 0.5 mm), as long as it isacoustically detectable as a moved reflection in the time domain. Inspecific embodiments, the axial deflection is less than about 1 mm underan axial force of less than about 100 grams. The bending deflection isless than about 10 degrees under a bending moment of about 200gram-millimeters (e.g., 100 grams applied at 2 mm moment arm distancefrom the tip spring member 304, 2 mm being the likely length of themost-distal tip portion 302 a).

As taught in the earlier disclosure, one monitors the echo reflectionsfrom the surface of the mirror 307 in order to deduce and back-computedeflections of the stiff spring 304. Two or more deflections may beevaluated in order to provide a vector sum and subcomponents of the netvector sum tip force. The mirror echoes are preferably significantlyweaker (e.g., 5-20 times) than the tissue echoes and arrive at anearlier time so that they can be differentiated from each other.

In the typical case the practitioner or doctor would, at a given moment,be using either the forward firing or the side firing transducerdepending on which has the best view of the tissue portion to belesioned. In FIG. 3, the lesion 312 is best viewed by the side-firingtransducer 305 b and its redirected beam 309 a/309 b. The lesion 312 isregarded as a sideways lesion as opposed to an end-on lesion. The systemused to control the catheter could automatically acoustically recognizethat there is tissue in front of (in the beamline of) a given transducer305 a or 305 b and switch over to that transducer.

The described embodiments, as those familiar with acoustics willrecognize, typically have the mirror or mirror and window/membrane inthe near-field of the transducer beam pattern. Inventors explicitlyinclude in their scope embodiments operating in the beams far-field aswell. It will be appreciated that near-field operation may allow for ashorter tip which is preferable.

Herein we have taken the liberty of giving force as grams which is oftendone for tip forces; however, the astute and technically correct readerwill understand that such practitioners mean grams-force and notgrams-mass. That is, the force or weight of a 1 gram mass is onegram-force in earth gravity.

While specific embodiments have been illustrated and described in thisspecification, those of ordinary skill in the art appreciate that anyarrangement that is calculated to achieve the same purpose may besubstituted for the specific embodiments disclosed. This disclosure isintended to cover any and all adaptations or variations of the presentinvention, and it is to be understood that the terms used in thefollowing claims should not be construed to limit the invention to thespecific embodiments disclosed in the specification. Rather, the scopeof the invention is to be determined entirely by the following claims,which are to be construed in accordance with the established doctrinesof claim interpretation, along with the full range of equivalents towhich such claims are entitled.

What is claimed is:
 1. An ablation catheter with acoustic monitoring,the ablation catheter comprising: an elongated catheter body extendinglongitudinally between a proximal end and a distal end along alongitudinal axis; a distal member disposed adjacent the distal end, thedistal member including an ablation element to ablate a biologicalmember at a target region outside the catheter body; one or moreacoustic transducers disposed in the distal member and each configuredto direct an acoustic signal toward a respective target ablation regionand receive reflection echoes therefrom; and an acoustic redirectionmember disposed in the distal member to at least partially redirect theacoustic signal from at least one of the acoustic transducers toward atissue target; wherein the distal member includes a most-distal portion,a proximal portion, and a deflectable portion between the most-distalportion and the proximal portion to permit deflection between themost-distal portion and the proximal portion of the distal member, thedeflectable portion being more deflectable than at least one of themost-distal portion or the proximal portion; and wherein (i) the one ormore acoustic transducers are mounted to the most-distal portion and theacoustic redirection member is mounted to the proximal portion, or (ii)the one or more acoustic transducers are mounted to the proximal portionand the acoustic redirection member is mounted to the most-distalportion of the distal member.
 2. The ablation catheter of claim 1,wherein the most-distal portion of the distal member has no axialdeflection and no bending deflection occurring within its own confines.3. The ablation catheter of claim 1, wherein the proximal portion of thedistal member has no axial deflection and no bending deflectionoccurring within its own confines.
 4. The ablation catheter of claim 1,wherein the deflectable portion of the distal member, within its ownconfines, permits at least one of axial deflection along thelongitudinal axis or bending deflection between the most-distal portionand the proximal portion of the distal member.
 5. The ablation catheterof claim 4, wherein the axial deflection is less than about 1 mm underan axial force of less than about 100 grams.
 6. The ablation catheter ofclaim 4, wherein the bending deflection is less than about 10 degreesunder a bending moment of about 200 gram-millimeters.
 7. The ablationcatheter of claim 1, wherein the deflectable portion of the distalmember includes one of a laser machined metallic tube with cuts, ametallic tube with cuts machined by wet etching, a metallic tube withcuts machined by EDM (electric discharge machining), a polymeric tube, abraided tube, a woven tube, a convoluted tubular member, a mesh tube, ahoneycombed tube, a wave washer, or a tubular member having bellows. 8.The ablation catheter of claim 1, wherein at least one of the acoustictransducers is configured to detect a deflection via at least one of anamplitude change or a phase or time-delay change of a reflection of anacoustic signal reflected back from the acoustic redirection member. 9.The ablation catheter of claim 1, further comprising: an acousticreflection member being mounted to the same portion of the distal memberas the acoustic redirection member and being configured to partiallyreflect an acoustic signal from at least one acoustic transducer of theacoustic transducers back to the at least one acoustic transducer;wherein the at least one acoustic transducer is configured to detect adeflection via at least one of an amplitude change or a phase ortime-delay change of a reflection of the acoustic signal reflected backfrom the acoustic reflection member.
 10. The ablation catheter of claim9, wherein the acoustic reflection member comprises one of a partiallyreflective membrane or a partially reflective prism.
 11. The ablationcatheter of claim 1, further comprising: a controller operable todetermine, based on the detected deflection and a relatedforce-deflection relationship of the deflectable portion of the distalmember, a force between the distal member and the biological member. 12.The ablation catheter of claim 1, wherein the acoustic signal comprisesan acoustic beam or an acoustic ping.
 13. The ablation catheter of claim1, wherein the one or more transducers comprise a sideways-redirectedacoustic transducer to produce an acoustic signal that is redirected ina beam emanation direction nonparallel to the longitudinal axis tomonitor a sideways-formed lesion, and a forward-directed acoustictransducer to produce another acoustic signal that is directed inanother direction generally parallel to the longitudinal axis to monitora forward-facing lesion, respectively.
 14. An acoustic monitoring methodfor an ablation procedure using an ablation catheter which includes anelongated catheter body extending longitudinally between a proximal endand a distal end along a longitudinal axis; a distal member disposedadjacent the distal end, the distal member including an ablation elementto ablate a biological member at a target region outside the catheterbody; one or more acoustic transducers disposed in the distal member andeach configured to direct an acoustic signal toward a respective targetablation region and receive reflection echoes therefrom; and an acousticredirection member disposed in the distal member to at least partiallyredirect the acoustic signal from at least one of the acoustictransducers toward a tissue target; wherein the distal member includes amost-distal portion, a proximal portion, and a deflectable portionbetween the most-distal portion and the proximal portion to permitdeflection between the most-distal portion and the proximal portion ofthe distal member, the deflectable portion being more deflectable thanat least one of the most-distal portion or the proximal portion; wherein(i) the one or more acoustic transducers are mounted to the most-distalportion and the acoustic redirection member is mounted to the proximalportion, or (ii) the one or more acoustic transducers are mounted to theproximal portion and the acoustic redirection member is mounted to themost-distal portion of the distal member; the method comprising:ablating the biological member at the target region with the ablationelement; directing one or more acoustic signals to the biological memberand receiving reflection echoes from the biological member by the one ormore acoustic transducers, the one or more acoustic signals including anacoustic signal directed toward the tissue target by the acousticredirection member; and detecting a deflection between the most-distalportion and the proximal portion of the distal member based onreflection of an acoustic signal reflected back to at least one of theacoustic transducers.
 15. The acoustic monitoring method of claim 14,wherein the detecting comprises: detecting a deflection via at least oneof an amplitude change or a phase or time-delay change of a reflectionof an acoustic signal reflected back from the acoustic redirectionmember to at least one of the acoustic transducers.
 16. The acousticmonitoring method of claim 14, wherein the detecting comprises:detecting a deflection via at least one of an amplitude change or aphase or time-delay change of a reflection of an acoustic signalreflected back from an acoustic reflection member to at least one of theacoustic transducers, the acoustic reflection member being mounted tothe same portion of the distal member as the acoustic redirection memberand partially reflecting the acoustic signal back to the at least oneacoustic transducer.
 17. The acoustic monitoring method of claim 14,further comprising: determining, based on a detected deflection and arelated force-deflection relationship of the deflectable portion of thedistal member, a force between the distal member and the biologicalmember.
 18. The acoustic monitoring method of claim 14, wherein theacoustic signal comprises an acoustic beam or an acoustic ping.
 19. Theacoustic monitoring method of claim 14, wherein the directing comprisesat least one of: directing a first acoustic signal from a first acoustictransducer in a direction generally parallel to the longitudinal axis tothe acoustic redirection member which redirects the first acousticsignal in a transverse direction nonparallel to the longitudinal axis tomonitor a sideways-formed lesion; or directing a second acoustic signalfrom a second acoustic transducer in a forward direction generallyparallel to the longitudinal axis to monitor a forward-facing lesion.20. The acoustic monitoring method of claim 14, wherein directing one ormore acoustic signals to the biological member and receiving reflectionechoes from the biological member by the one or more acoustictransducers comprises at least one of acoustic lesion feedback of thebiological member being ablated, a tissue thickness measurement in aregion of the biological member being ablated, a tissue proximitymeasurement in a region of the biological member being ablated, apre-pop warning of the biological member being ablated, or a pre-popdetection of the biological member being ablated.
 21. The acousticmonitoring method of claim 14, wherein the deflectable portion of thedistal member permits at least one of axial deflection along thelongitudinal axis or bending deflection between the most-distal portionand the proximal portion of the distal member.
 22. The acousticmonitoring method of claim 21, wherein the axial deflection is less thanabout 1 mm under an axial force of less than about 100 grams.
 23. Theacoustic monitoring method of claim 21, wherein the bending deflectionis less than about 10 degrees under a bending moment of about 200gram-millimeters.